Loudspeaker diaphragm for use in electroacoustic transducer containing Kenaf fibers

Abstract: A loudspeaker diaphragm is obtained with a fibrous material containing at least a kenaf fiber as a substitute for wooden fiber, the material being subjected to paper-making steps. The loudspeaker diaphragm thus manufactured with such non-wooden fiber can be made to closely resemble the one manufactured with the wooden fiber, to be light in weight, high in the rigidity and internal loss and still low in manufacturing costs.

Description: Field of Utilization in Industry This invention relates to improvements in a paper-made loudspeaker diaphragm for use in electroacoustic transducers. Prior Art For the loudspeaker diaphragm, in general, it is demanded to have such excellent solid state properties that the density is small to be high in the elasticity, a proper internal loss is provided, no mechanical fatigue is provided while excellent in the weathering properties. While various ideas have been suggested to use to satisfy the foregoing solid state properties, a variety of high polymer materials, metallic materials, ceramic materials they are all troublesome in respect of the control of the foregoing solid state properties and manufacturing complexity, and are high in the manufacturing costs. On the other hand, the paper-made loudspeaker diaphragm has been frequently utilized because of an easiness of the control of the foregoing solid state properties and of the manufacture. Dynamical properties of this paper-made loudspeaker diaphragm are determined by the solid state properties of single fiber employed, or by coupling strength and coupling area between fibers. While wooden pulp has been generally employed as the material for the currently employed paper-made loudspeaker diaphragm from the viewpoint of costs, on the other hand, the reckless deforestation is mentioned in recent years as a problem in respect to the terrestrial environmental destruction. Since in this case global warming and desertizing phenomena can be prevented by means of conservation of forest, it has become an important theme to reconsider non-wooden paper resources. For the purpose of the conservation of forestal resources, therefore, it has been demanded to provide a substitute material for wood so as to reduce the amount of wood used. In contemplating a remakable reduction in the amount of wood used for the purpose of the conservation of the forestal resources taking into account the restriction of the terrestrial environmental destruction, it may be first mentioned to utilize reclaimed paper. However, used paper is generally stocked outdoor so as to be deteriorated due to such various factors as rainwater, sunshine, decomposing fungi and so on, and the employment of the used paper placed under such conditions involves a problem particularly in respect of the obtainment of the high rigidity when such paper is used for making the diaphragm, and it is difficult to obtain a loudspeaker diaphragm having uniform solid state properties. It is possible on the other hand to employ such tubular fibrous bundle fiber as straw, bamboo and Manila hemp as the non-wooden fiber in making the loudspeaker diaphragm, whereas, when these materials are used, there arises a problem that satisfactory solid state properties and tone cannot be obtained with the thus made loudspeaker diaphragm employed in the acoustic products. Further, there has been also employed for the paper-made loudspeaker diaphragm such bast fiber as paper mulberry, Edgeworthia papyrifera of flax, but there has been involved a problem that the same has been poor in the productivity so as to be expensive. Technical Field Consequently, an object of the present invention is to provide a loudspeaker diaphragm for use in the electroacoustic transducers, which is manufactured on the premiss that the non-wooden fiber is employed and yet can be a sufficient substitute for the one made of the wooden fiber, and is excellent in the productivity to be inexpensive. As the result of keen study made by the present inventors, it has been found to be extremely useful to employ kenaf fiber as the substitute material for wood. Kenaf is an annual plant which has a remarkably shorter rearing period than wood and can be reared even on wasteland, and its fibrous characteristics and eventually its solid state properties when used in the loudspeaker diaphragm are closely resembling the wooden fiber. Here, fibrous length and width of pulps of whole kenaf stalks, kenaf bast, bleached kraft (LBKP), Manila hemp and wood (NBKP) are shown in the following Table I: Type of Pulp Fibre Length (mm) Fibre Width (µm) Whole kenaf stalk 1.28 34 Kenaf bast 2.5 23 LBKP 1 to 2 20 Manila hemp 2 to 8 16 to 32 NBKP 2 to 4 30 A paper-made loudspeaker diaphragm according to the present invention employing the kenaf fiber among the materials in the above Table shows to be light in weight and high in rigidity and to have a high internal loss, and can be contributive to the restriction of the terrestrial enviromental destruction. In order to establish the above purpose, according to the present invention, the loudspeaker diaphragm is manufactured by subjecting the kenaf fiber alone or mixed with other fibrous material to paper-making step. In another embodiment of the present invention, a moisture-proofing or a waterproofing is carried out with respect to the foregoing loudspeaker diaphragm. Function The solid state properties of kenaf fiber show, when used as the material for the loudspeaker diaphragm, values equal to or more desirous than those of the wooden fiber, and can provide substantially the same characteristics as the paper-made loudspeaker diaphragm comprising the wooden fiber. Embodiment The present invention will now be further elucidated with reference to an embodiment. Here, the kenaf pulp employed in the present invention is prepared in the manner described later. That is, as the seeds, a "Blue Skin" No. 3 produced in China and "Everglade" (EG) Nos. 41 and 47 produced in U.S.A. were employed, these seeds were reared in Japan to obtain kenaf, which plant after the harvest was dried sufficiently, chipped to be about 5cm long in the fibrous material, and pulped while separating into a bast part and a woody part. Conditions for preparing a kraft pulp were as stated hereafter. That is, the degree of xanthation was 25%, effective alkali was 16%, liquid ratio was 1:7, digesting temperature was 170°C, digesting time was 3.5 hours and Rohe value was 3.2, upon which the total yield was 48%. Here, bleached kenaf kraft pulp and the one obtained by subjecting this kraft pulp to a beating with PFI mill were employed, they were formed into a sheet through hand papering, and the solid state properties were evaluated mainly by Vibration Lead method. In this case, there were prepared as samples a sheet containing the "Blue Skin" No. 3, a sheet containing EG-41 and a sheet containing EG-71, and results of measurement with respect to each of them were as shown in Table II. As will be clear from Table II, it has been found that the solid state properties when employed in the respective loudspeaker diaphragms show desirable values more than equal to those of the wooden pulp (NBKP). Further, other than the above properties, it has been found that the kenaf pulp has the following features: (1) It shows lower water absorption and oil permeability than NBKP, and has a water-resisting and oil-resisting effect. (2) When used as mixed and papered with the wooden pulp, it increases the bulk, and the rigidity as the loudspeaker diaphragm is improved. (3) It is possible to use the kenaf pulp as the loudspeaker diaphragm even without it being subjected to the beating. (4) When employed as beat, the beating proceeds faster than the wood pulp, and an energy saving can be attained upon the production. Further, a loudspeaker diaphragm was prepared by employing a pulp made with the woody part in the foregoing sample EG-71 kept non-beat, upon which alkyl ketene dimer (ACOPEL 12 made by DICK-HERCULES K.K.) was used as a sizing agent. The thus prepared loudspeaker diaphragm according to the present invention and a loudspeaker diaphragm prepared with the wooden pulp and formed into mutually the same shape were each employed respectively to construct loudspeakers of a diameter of 10cm, and they were subjected to a measurement of high frequency characteristics. As the result, as shown in an accompanying drawing, the loudspeaker employing the kenaf pulp diaphragm has shown such frequency characteristics as represented by a broken line Q, comparable with such frequency characteristics as represented by a solid line P of the loudspeaker employing the wooden pulp (NBKP). It is also effective to carry out the moistureproofing and waterproofing with respect to the loudspeaker diaphragm, so that the diaphragm can be provided with sufficient moisture resistance and water resistance so as to have good aptitude for use in many foreign countries in which high temperature and high humidity prevail. Effect of the Invention According to the present invention of the foregoing arrangement, the loudspeaker diaphragm employing the kenaf pulp has the solid state properties of desirable values equal to or more than the loudspeaker diaphragm employing the conventional wooden pulp, so that there can be realized such effect that the loudspeaker diaphragm of light weight, high rigidity and high internal loss can be obtained, and the wood is made unnecessary by the employment of the kenaf pulp so as to be able to attain the conservation of forestry resources and to be effectively contributive to such restriction of the terrestrial environmental destruction as the prevention of global warming and desertizing phenomena. 4. Brief Explanation of the Drawing: The drawing is a frequency characteristics diagram with respect to the sound pressure of the loudspeaker employing the diaphragm in an embodiment according to the present invention and the loudspeaker employing the conventional wooden pulp.

Claims: A loudspeaker diaphragm comprising a fibrous material characterized in containing at least a kenaf fiber resulting from a paper-making step. A loudspeaker diaphragm according to claim 1, wherein said kenaf fiber is used alone as said fibrous material. A loudspeaker diaphragm according to claim 1, wherein said fibrous material contains said kenaf fiber and another fiber. A loudspeaker diaphragm according to any one of claims 1 to 3, with is moisture proof. A loudspeaker diaphragm according to any one of claims 1 to 3, which is waterproof.

Inventors: ICHIKAWA HIDEKAZU, MIKUNIYA TAKASHI, MOTOHASHI HIDEAKI, MUSHA MUTSUO, ICHIKAWA, HIDEKAZU, MIKUNIYA, TAKASHI, MOTOHASHI, HIDEAKI, MUSHA, MUTSUO, ICHIKAWA, HIDEKAZU, C/O FOSTER ELECTRIC CO., LTD., MIKUNIYA, TAKASHI, C/O FOSTER ELECTRIC CO., LTD., MOTOHASHI, HIDEAKI, C/O FOSTER ELECTRIC CO., LTD., MUSHA, MUTSUO, C/O FOSTER ELECTRIC CO., LTD.
Applicants: FOSTER ELECTRIC CO LTD, FOSTER ELECTRIC CO., LTD.
Application year: 1994
Main classification: H04R7
IPC codes: D21C5, B32B29, H04R7